placement of power conditioner

I keep all my power gear (conditioner & power supplies) on bottom shelf. I would never put any equipment on the floor.

If you think your surrounding equipment has adequate shielding, then go for it.

If you have a decent PLC I don't think it matters where you place it. In the rack, on the floor, on a platform, etc. The latter is what I do with mine. Sometimes it amounts only to a piece of MDF, OR hardwoods.

To some degree I've found the surface on which one is placed can or may affect the sound some. In addition to the wood thingy's I also use compliant polymer footers underneath them for further isolation. They work on stuff which doesn't rotate too.

the only other thought is if the PLC gets hot. If so, I'd sure put something under it if on the carpeting, or throw it in the rack and find out if it'll affect things... then all you have to do is re-route power cords.